1. Field of the Invention
Embodiments of the present disclosure generally relate to an apparatus for providing phase rotation for a three-phase AC circuit.
2. Description of the Related Art
Solar panels have historically been deployed in mostly remote applications, such as remote cabins in the wilderness or satellites, where commercial power was not available. Due to the high cost of installation, solar panels were not an economical choice for generating power unless no other power options were available. However, the worldwide growth of energy demand is leading to a durable increase in energy cost. In addition, it is now well established that the fossil energy reserves currently being used to generate electricity are rapidly being depleted. These growing impediments to conventional commercial power generation make solar panels a more attractive option to pursue.
Solar panels, or photovoltaic (PV) modules, convert energy from sunlight received into direct current (DC). The PV modules cannot store the electrical energy they produce, so the energy must either be dispersed to an energy storage system, such as a battery or pumped hydroelectricity storage, or dispersed by a load. One option to use the energy produced is to employ inverters to convert the DC current into an alternating current (AC) and couple the AC current to the commercial power grid. In this type of system, the power produced by the solar panels can be sold to the commercial power company.
Traditionally, solar systems have used centralized inverters, where many PV modules feed into a single large inverter for the conversion of DC current to AC current in applications such as the one described above. A recent trend has been to decentralize this DC/AC conversion by using micro-inverters. Rather than employing a single large inverter, a micro-inverter is individually coupled to each PV module. Micro-inverters improve the performance of the DC/AC power conversion by optimally extracting the maximum power from each PV module. Micro-inverters also offer the added benefit of using a connective wire bus that carries entirely AC voltage rather than the high voltage DC used in traditional centralized inverter systems, thereby offering improved safety and efficiency.
Micro-inverters are typically arranged in a string on a branch circuit from a load center. Additionally, there may be multiple branch circuits from the load center, where each branch circuit supports a string of micro-inverters and their associated PV modules. In large scale installations, it is common to use three-phase grid connections from the load center. It is not always economical though to have a true three-phase micro-inverter as it requires a substantially more electronics than a single-phase micro-inverter. Traditional methods of connecting single-phase micro-inverters in a three-phase grid connection requires three strings of micro-inverters, where each string is connected to two of the three power phases. In order to properly balance the load on each phase, an electrician needs to install the same number of micro-inverters on each branch circuit and needs to use equally all phases for all of the branch circuits. This leads to a need for extensive installation planning and longer and more cumbersome installations.
Therefore, there is a need in the art for an apparatus that can employ single-phase micro-inverters in three-phase grid connections in such a way that micro-inverter installation and load balancing on the three phases are greatly simplified.